Studies on an Antitumor Polysaccharide RBS Derived from Rice Bran. II. : Preparation and General Properties of RON, an Active Fraction of RBS

An antitumor polysaccharide RON was obtained by fractionating RBS (a saccharide derived from rice bran) as the non-adsorbed fraction on diethylaminoethyl-Sepharose CL-6B. RON is a dextran-like α-glucan composed mainly of α-1, 6-glucosidic linkages with a small amount of C-3 branches. Methylation analysis showed that the molar ratio of non reducing terminal : 1, 6-linkage : 1, 3, 6-linkage was 1 : 25 : 1.2. Its molecular weight is over 1000 kilodaltons (kDa), the specific rotation is [α]20D +205°, it contains almost no protein and no starch, and it contains a small amount of inorganic substances.RON has potent antitumor activities against syngeneic tumors, Meth-A fibrosacoma and Lewis lung carcinoma not only by intraperitoneal administration but also by oral administration, having optimum doses around 30 mg/kg. It is rare that an α-glucan such as RON has potent antitumor activities. Therefore, RON could be an interesting material to elucidate the relationship between the structure and antitumor activities of polysaccharides.